Laser bars are fast becoming a key device in a range of specific industrial applications. Mechanical cleavage technology is a new and efficient method for fabricating laser bars. However, there is little detailed analysis of the relationship between scratching step and cleavage step. To close this research gap, a molecular dynamics study on cleavage mechanisms of GaAs are reported investigating surface and subsurface damage, and molecular dynamics method could accurately describe the nano-scale processes in semiconductors at atomic scale. Simulation results show that the scratching depth has a significant effect on the scratch quality as compared with other parameters during the scratching process. Then, a series of cleavage experiments were carried out to verify the simulation results and further explore the influence of key scratching parameters on cleavage plane morphology. Experimental results correlate well with the simulations. Consequently, the achieved optimal combination of parameters have been found to be a scratching load of 10 g, scratching speed of 20 mm/s and scratching length of 0.6 mm, which provides direct guidance for the cleavage processing of GaAs materials. Under optimal conditions, the length and surface roughness of the undamaged area can reach 11.77 mm and 0.43 nm respectively.